Conventionally, a hair bleach product and a hair dye product are widely available in the form of liquid or cream. However, it is difficult for those who are not accustomed to using such a product to evenly apply it to the hair. This is because the viscosity of a mixture to be applied to the hair is adjusted relatively high, namely, to approximately 1,000 to 10,000 mPa·s, for prevention of dripping while the mixture is left on the hair. This makes it difficult to evenly spread the mixture and to adequately cover the hair root with the mixture. Furthermore, skills such as blocking and two-mirror technique are necessary for application of the mixture to the hair root and the back of the head, also requiring much time.
In contrast, a non-aerosol type foamer container discharging a liquid mixture of a two-part hair bleach or a two-part hair dye contained therein in the form of a foam is proposed (Patent Document 1). The above hair bleach product or hair dye product discharges a liquid mixture of the first part and the second part from a non-aerosol type foamer container in the form of a foam, whereby the liquid mixture is evenly applied to the hair, resulting in an evenly-colored finish. The above hair bleach product or hair dye product is particularly useful for resolving color differences between a newly-grown part and an already-dyed part. For these reasons, it is supported by a wide range of customers, regardless of sex and age groups.
However, the two-part hair bleach and the two-part hair dye in the form of a foam of Patent Document 1 have various problems peculiar to the product in the form of a foam discharged from a non-aerosol type foamer container such as reduced foaming properties at low temperature. Also, because such a hair dye product has extremely lower viscosity in the state of a liquid mixture as compared to a conventional liquid or cream (hereinbelow, referred to as “conventional type”) hair dye product, there has also been a limitation that a composition having good storage stability has to be designed. Furthermore, the two-part hair bleach and the two-part hair dye in the form of a foam of Patent Document 1 tend to have less sufficient fastness to shampooing than does a conventional type. This is considered to be attributable to the following reasons: because the hair dye product is applied to the hair in the form of a foam, the amount of the hair dye directly contributing to dyeing is smaller than the amount of the hair dye actually applied, and also, because the area of the air-liquid surface of the above product is larger than that of a conventional type, ammonia serving as an alkali agent readily volatilizes, leading to an insufficient amount of the alkali agent for full penetration of the dye into the center of the hair.
In contrast, as a conventional type two-part hair dye, a two-part hair dye containing polyoxyalkylenated carboxylic acid ether or a salt thereof and a cationic polymer or an amphoteric polymer having no less than a certain level of cationic charge density is proposed (refer to Patent Document 2). According to this literature, the two-part hair dye disclosed therein can impart a favorable hue. However, there is no description pertaining to a two-part hair dye provided in the form of a foam by using a non-aerosol type foamer container discharging a liquid mixture contained therein. Further, this literature is also totally unsuggestive of a problem peculiar to the two-part hair dye in the form of a foam such as low foaming properties at low temperature and a problem peculiar to a two-part hair dye prepared in the aforementioned form such as storage stability and fastness to shampooing.
Also, a less irritating shampoo composition containing alkyl ether acetate and a cationic polymer exhibiting excellent hair color fading-preventing effects, foaming, smoothness when running fingers through the hair while shampooing, and smoothness during rinsing is proposed (Patent Document 3). However, this literature neither describes nor suggests the mole fraction of the cationic monomer in the cationic polymer. Further, provided that this literature pertains to an invention relating to a shampoo composition, there is no question that it is totally silent on application to a hair dye product. In the first place, this invention relates to a technique to achieve prevention of color fading of the hair dyed with a hair color by use of this shampoo composition, and irrespective of the shampoo used, the technical idea per se is entirely unrelated to provision of a hair dye product excellent in fastness to shampooing.    [Patent Document 1] JP-A-2004-339216    [Patent Document 2] JP-A-2003-192551    [Patent Document 3] JP-A-2001-131034